1. Field of the Invention
The present invention relates to a polyacetal resin composition. More particularly, the present invention relates to a polyacetal resin composition superior in water resistance at high temperatures.
2. Prior Art
Polyacetal resins are superior in mechanical strengths, sliding property, heat resistance, chemical resistance, moldability and electrical properties; therefore, they are used in wide applications as an engineering plastic. Polyacetal resins, however, are not fully satisfactory in acid resistance, adhesivity, coatability, printability, dyeability, weatherability, water resistance at high temperatures, etc. Hence, various studies have been made in order to alleviate these drawbacks of polyacetal resin.
In order to improve, for example, the adhesivity, coatability and dyeability of a polyacetal resin, it is effective to introduce a modifying group into the polyacetal resin to modify the polyacetal. As the method for improvement of polyacetal resin by introduction of such a modifying group thereinto, there were proposed, for example, a method (disclosed in JP-B-43-23467) of introducing an amino group by using aminoaldehyde as a comonomer; and a method (disclosed in JP-B47-19425) of using, as a comonomer, a nitro group-containing cyclic ether or cyclic acetal and reducing the nitro group to convert it into an amino group.
There were also proposed a method (disclosed in JPA-3-21618 and JP-A-3-21619) of producing a copolyacetal having hydroxyl group or the like, by using a comonomer; a method (disclosed in JP-A-5-25238) of copolymerizing a cyclic ether or cyclic formal having carboxyl group, amino group or the like, with trioxane; and a method (disclosed in JP-A-8-127631) of melt-kneading a polyacetal resin with a polymerizable compound to introduce a modifying group into the polyacetal resin.
Having good properties as mentioned above, polyacetal resins are used in the forms of, for example, miscellaneous clips including those for an electric wire, rivets for construction, miscellaneous screws including a radiator cock, gears, rollers, etc. In some cases, these members may be exposed to high temperatures and high humidities; however, there has been made no attempt of improving the high-temperature water resistance of polyacetal resin.